MATERIALS
TECHNOLOGY SECTION TECHNICAL
NOTE No. 19
Issued by the Manager, Materials Technology on September 2000
THE EFFECT OF WIND CHILL ON SPRAYING TEMPERATURE AND CUTTING OF BINDERS.
Part 225 of the Master Specification provides a cutting chart for the addition of cutter to binders for different pavement temperatures. The recommended added parts of cutter presuppose that there is little or no wind.
When there is a significant breeze blowing, the chill effect will mean that the binder will cool more rapidly, and some allowance should be made for it.
Unfortunately, there is seldom any means of measuring the wind speed on site, and, even if there was, the wind speed is liable to change between the times of measurement and spraying (and even during the spray run).
As a result of the above it is impossible to provide a rigid specification, but rather, provide some general guidance.
The effect of wind speed on pavement temperature is summarised in Table 1 below. It is this temperature that will indicate the amount of cutter should be added to the binder, as per Part 225 of the Master Specification.
Effect of wind chill on pavement temperature
Wind speed Km/h |
Air temperature <30oC |
Air temperature >30oC |
<19 |
Ignore |
Ignore |
20-38 |
Subtract 5oC from pavement temperature # |
Ignore |
>38 |
Do not spray * |
Do not spray * |
Notes:
# With some Polymer Modified Binders (SBS in particular), the effect of wind chill may drop the effective pavement temperature below the permissible spraying temperature, and, in such a case, SPRAYING SHOULD STOP.
* Wind speeds above 38Km/h will usually be so strong that they affect proper distribution of binder, and spraying should not be done.
The wind speed may be classified by a set of reasonably accepted general descriptions, each having it’s own indications, as set out in Table 2.
The above advice is practical and the best currently available. If it is followed sensibly, it will help to avoid costly mistakes. For further detail, seek specialist advice from your friendly Materials team.
TABLE 2
GUIDE TO WIND DESCRIPTIONS FOR WIND CHILL ALLOWANCES
Wind velocity km/h |
Wind velocity Knots |
Description |
Indications |
Comments |
0 - 1.5 |
0 - 1 |
Calm |
Smoke rises vertically. Water is like a mirror. |
No allowance necessary |
1.5 - 5 |
1 - 3 |
Light air |
Wind direction shown by smoke drift, but not by vanes. Ripples formed appear like scales. |
No allowance necessary |
6 - 11 |
4 - 6 |
Light breeze |
Wind felt on face; leaves rustle, vanes moved by wind. Small wavelets, still short, but more pronounced. |
No allowance necessary |
12 - 19 |
7 - 10 |
Gentle breeze |
Leaves and small twigs inconstant motion. Wind slightly extends flag. Large wavelets. |
No allowance necessary |
20 - 29 |
11 - 16 |
Moderate breeze |
Raises dust and loose paper. Small branches are moved. Small waves, becoming larger. |
Allowance needed if air temp <30oC |
30 - 38 |
17 - 21 |
Fresh breeze |
Small trees in leaf begin to sway. Crested waves form on inland waters. |
Allowance needed if air temp <30oC |
39 - 50 |
22 - 27 |
Strong breeze |
Large branches in motion. Whistling heard in wires. Umbrellas used with difficulty. |
Spraying not advised |
51 |
28 |
Near gale or Gale, Storm etc |
Whole trees in motion. Inconvenience felt when walking against the wind. |
DO NOT SPRAY |
Surfacings Engineer, Robert Busuttil (08) 82600544
Compiled
by Trevor Clark and Robert Busuttil, Road Surfacings Unit Page
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